AP BIOLOGY

Detailed explanation-1: -In population genetics, directional selection, is a mode of negative natural selection in which an extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype.

Detailed explanation-2: -The directional selection theory says that an extreme phenotype (characteristics or traits) is favored over other phenotypes and this causes the allele frequency (how often the variant of a gene shows up in a population) to shift over time in favor of the extreme phenotype.

Detailed explanation-3: -Theoretical models predict that under directional selection, phenotypic (co)variation should evolve in step with the underlying adaptive landscape, increasing the degree of correlation among co-selected traits as well as the amount of genetic variance in the direction of selection.

Detailed explanation-4: -Directional selection shifts the curve towards the favorable phenotype. Disruptive selection. Both extreme phenotypes are more fit than those in the middle.

Detailed explanation-5: -Directional selection occurs when individuals with traits on one side of the mean in their population survive better or reproduce more than those on the other. It has been demonstrated many times in natural populations, using both observational and experimental approaches.